Romiplostim N01 for Chemotherapy-Induced Thrombocytopenia in Pediatric Cancer Patients

The goal of this clinical trial is to evaluate the efficacy and safety of romiplostim N01 in treating chemotherapy-induced thrombocytopenia (CIT) in children and adolescents/young adults (CAYA; aged 6-24 years) with hematologic malignancies or solid tumors. The main questions it aims to answer are: * What proportion of participants achieve platelet count recovery (≥100×10⁹/L or an increase of ≥30×10⁹/L from baseline) within 3 weeks of romiplostim N01 treatment? * What is the safety profile of romiplostim N01 in this population, including the incidence and severity of adverse events (especially bleeding and thrombosis)? This is a single-arm study (no comparison group). Researchers will assess the outcomes against predefined efficacy thresholds and historical data (e.g., a 60.7% response rate reported for another TPO-RA, hetrombopag). Participants will: * Receive weekly subcutaneous injections of romiplostim N01 (starting dose: 2 µg/kg). * Have their romiplostim dose adjusted weekly based on platelet counts (increase by 1-2 µg/kg if platelets \<99×10⁹/L, maximum dose 10 µg/kg, stop when target recovery is met). * Undergo frequent monitoring, including blood tests (especially platelet counts), vital signs, physical exams, and assessment for adverse events and bleeding throughout the treatment and follow-up period.